1. Field of the Invention
The present invention relates to a diamond heat sink. More particularly, a diamond heat sink is produced to contain diamond made by chemical vapor deposition.
2. Background Information
A heat sink (radiator) is adapted to efficiently dissipate heat which is generated in operation of a device such as a semiconductor laser diode, and LED (light emitting diode), a semiconductor high frequency device or the like. The material for such a heat sink is selected in accordance with the heat produced by the device to which the heat sink is applied. Table 1 shows physical properties to various heat sink materials.
TABLE 1 __________________________________________________________________________ Monocry- Vapor- cBN Physical stalline Deposited Sintered Properties Diamond Diamond Body Cu Sic Cu--W BeO AlN Si __________________________________________________________________________ Density 3.52 3.52 3.49 8.9 3.1 16.4 2.9 3.26 2.3 (g/cm.sup.2) Vickers Hardness 12,000 12,000 6,000 80 -- 260 1,200 1,200 -- (kg/mm.sup.2) Transverse 400 200 -- -- 40 136 20 30 -- Rapture Strength (kg/mm.sup.3) Thermal 2,000 1,000 600 390 270 250 250 200 140 Conductivity (W/m .multidot. K) Thermal Expansion 2.3 -- 3.7 16.5 3.7 8.5 7.6 4.5 4.2 Coefficient (.times.10.sup.-6 /.degree.C.) Specific Heat 0.122 -- -- 0.092 -- 0.044 0.25 0.16 0.18 (cal/g .multidot. .degree.C.) Electric 10.sup.16 5 .times. 10.sup.9 10.sup.11 1.7 .times. 10.sup.-6 10.sup.13 3.4 .times. 10.sup.-6 10.sup.15 10.sup.13 2.3 .times. 10.sup.5 Resistivity (.OMEGA. .multidot. cm) Dielectric 5.7 6.5 6.5 -- 40 -- 6.7 8.9 -- Constant (1 MH.sub.2) __________________________________________________________________________
As shown in Table 1, diamond has a high thermal conductivity. Therefore, a diamond heat sink is employed as a heat dissipating part for a device having a high heating value such as high power semiconductor lasers for communication, optical memories solid state laser pumping devices or the like, for example. Presently, such a diamond heat sink is mainly made of natural or synthetic monocrystalline diamond.
FIG. 7 is a process diagram successively showing steps in conventional methods of manufacturing diamond heat sinks. Referring to FIG. 7, a monocrystalline diamond material is prepared by high pressure synthesis or the like (step 601). According to a first manufacturing method, this monocrystalline diamond material is cut into chips with a diamond saw (step 610). The cut diamond chips are arranged side by side with no clearances and metallized (step 611), so that only upper and bottom surfaces of each diamond chip are metallized.
According to a second manufacturing method, on the other hand, a monocrystalline diamond material is cut into chips with a diamond saw (step 610), similarly to the first manufacturing method. Each of the cut diamond chips is metallized on all faces (step 612). Side surfaces of the entirely metallized diamond chip are ground with a diamond grindstone (step 613), so that metallized films are left only on upper and bottom surfaces of the diamond chip.
According to a third manufacturing method, a monocrystalline diamond material is metallized before cutting (step 620). The metallized monocrystalline diamond material is cut with a diamond saw into chips, each of which is then cut into a final shape (step 621).
Conventional diamond heat sinks are manufactured in the above manners.
In each of the aforementioned conventional methods of manufacturing diamond heat sinks, a monocrystalline diamond material is cut with a diamond saw. Therefore, the diamond material cannot be cut with a high accuracy, and the cutting speed is very slow. Further, a great deal of waste results from the cutting and grinding steps, leading to an inferior yield. Thus, a diamond heat sink cannot be easily manufactured by a conventional method, leading to inferiority in mass productivity.
On the other hand, each of Japanese Patent Laying-Open Nos. 2-268917 (1990) and 3-138106 (1990) discloses a method of working a monocrystalline diamond material without using a diamond saw.